Section 57(4)(b) in The Indian Port Health Rules, 1955
(b)At any port approved for issuing Deratting Exemption Certificates only the Health Officer may issue such a certificate if he is satisfied that the number of rodents on board is negligible. Such a certificate shall be issued only if the inspection of the ship has been carried out when the holds are empty or when they contain only ballast or other material unattractive to rodents, of such a nature or so disposed as to make a through inspection of the holds possible. A Deratting Exemption Certificate may be issued for an oil-tanker with full holds.